Ouch, seen a few broken flexplates over the years, but in all the years and miles, including 31 as a Trooper with over a million miles in a state patrol pursuit vehicle ..... I never actually had one break for me.

Did replace one in a '70 Chevrolet CST-10 PU with BBC and T-400 because the ring gear had a bad spot though. It was 2 WD so I used two long 3/8 bolts (one each side through bellhousing into block) and slid the trans and cross member back far enough to replace it without dropping anything except the driveshaft.

 

I had the same issue! The newer one on the right broke after only a couple days after replacing the old one. The old one has worn teeth. Rock Auto would only give me another atp replacement and I’m terrified it’ll bust again.